1. Field of the Invention
The present invention relates to a wideband antenna, and more particularly, to a wideband antenna capable of uniformly distributing current on a low-frequency radiating element to obtain better omnidirectional radiation and increase the low frequency bandwidth.
2. Description of the Prior Art
An electronic product having a communication function, such as a laptop computer, a personal digital assistant, etc., uses an antenna to transmit or receive radio waves, so as to transfer or exchange radio signals, and access wireless network. Therefore, in order to let a user to access wireless network more conveniently, a bandwidth of an ideal antenna should be extended as broadly as possible within a tolerable range, while a size thereof should be minimized as much as possible, to meet a main stream of reducing a size of the electronic product.
Planar Inverted-F Antenna (PIFA) is a monopole antenna commonly used in a radio transceiver device. As implied in the name, a shape of PIFA is similar to an inverted and rotated “F”. PIFA has advantages of low production cost, high radiation efficiency, easily realizing multi-channel operations, etc. However, a size or arrangement of PIFA is usually fixed, such that input and output impedances of the antenna cannot be easily adjusted. Therefore, in order to improve abovementioned drawbacks, applicant of the present invention has provided a dualband antenna 10 in U.S. Pat. No. 6,861,986, as shown in FIG. 1. The dualband antenna 10 has a simplified structure, and can reduce the number of strips efficiently.
With developments of a variety of wireless communication systems, transmission efficiency of a low frequency band is requested. Therefore, to increase the low frequency bandwidth of the dualband antenna 10 is a goal the applicant works for.